Objective: This qualitative interview study explored perceptions of the phrases ‘population health’, ‘public health’ and ‘community health’. Setting: Accountable care organisations (ACOs), and public health or similar agencies in different parts of the USA. Participants: Purposive sample of 29 interviewees at four ACOs, and 10 interviewees at six public health or similar agencies. Results: Interviewees working for ACOs most often viewed ‘population health’ as referring to a defined group of their organisation's patients, though a few applied the phrase to people living in a geographical area. In contrast, interviewees working for public health agencies were more likely to consider ‘population health’ from a geographical perspective. Conclusions: Conflating geographical population health with the health of ACOs’ patients may divert attention and resources away from organisations that use non-medical means to improve the health of geographical populations. As ACOs battle to control costs of their population of patients, it would be more accurate to consider using a more specific phrase, such as ‘population of attributed patients’, to refer to ACOs’ efforts to care for the health of their defined group of patients.